Low cost BMS

[Simy]

I'm not sure if what Paul is working on will do that but harlequin2's won't. What I plan on doing will, my thread is at "BMS/Master brain" Right below this one =)

My Desktop is down for the moment but I plan to post a block diagram soon, I just ordered a few chips, transistors, and LEDs and the pickit 3, got suckered into impatient shipping so it should be here Monday if not Tuesday =)

I need to play with it a bit to see how it all works then I can really get started. =) Suggestions are welcome....

Edit: But you could modify the hardware to have it work with SLA's

[harlequin2]

Originally Posted by sawickm

What type of battery does your BMS work with Lion or SLA? Both would be nice, most DIY'ers can only afford SLAs. All of the BMSs on the market are only for Lions.

It would be nice if you could also interface your master controller to "Adam's" open source 6Kw charger http://ecomodder.com/forum/240533-post37.html.

It would be great to see a ReVolt open source Motor Controller, DC Charger, BMS, and LCD Display all connect to each other as a complete system !!!

-Mark

It is designed for Li cells - they are what I am using and they are far less tolerant of abuse than SLAs, so a BMS is an imperative.

I could easily make it work with single SLA cells though, its just a software modification as the micro will work down to 1.8V quite happily. But SLAs are not usually used in single cell configuration, you just buy a 12V battery - attaching a board to each cell might be a bit tricky.
Having said that, I'm sure there are people out there who could do it!

I can't see much point in using a bms that doesn't monitor individual cells ie just looks at 12V batteries. Its a lot of trouble and expense to only do 1/6 of the job.

Maybe I'll put something in the s/w so the user can choose either SLA or Li, if there's any interest shown. Its only a matter of changing the range the ADC works over and altering the master s/w to suit.

I have a description of the way the whole thing works, but the .pdf file is way too big to add here as an attachment.

Unfortunately, Adam's charger design is quite illegal in most countries, including this one (New Zealand). I'd be surprised if it was legal in the US, but you never know!

My charger interface comprises a pair of normally open contacts and that is pretty universal in that you can make it work with anything.

As I said, it is my intention to modify the Cougar LCD design a bit and incorporate the bms master function into it, so that will be a big step towards having an integrated system. Initially, I am doing a stand alone version to make sure everything works as expected and to cater for those who don't have/need/want the Cougar LCD.

[ianbartie]

Hi Harlequin2
How does the PIC in your BMS module handle noise?
Is there a likelihood of a PIC lockup doing something like the following?

The reason I ask is because another guy I know made up the micro controlled BMS (with a couple of minor mods) on the Battery Vehicle Society web site.
It worked fine initially until the day either the master or some of the slaves locked up (can't remember which he said it was) apparently due to noise.
The BMS then didn't put out the Low Cell Voltage warning & 26 batteries got discharged to the point of being door stops as a result.
Wouldn't want that to happen to anyone's LiFePo pack.

[harlequin2]

The micro has a watchdog reset - if it gets glitched enough to stop that, it'll reset.
The comms is monitored and if it fails an alarm is generated.
I've tried a single module on a cell in my car and has worked just fine, so I don't see why a whole lot of them shouldn't work either. I have 45 pcbs on the way to prove it!

[ianbartie]

I'll be following this project with a great deal of interest.
My BMS is an analogue design that does cell monitoring with low voltage output that lowers the Cougar output, a high voltage limit that forces the charger to back off & a high voltage cut that cuts off the charging if any cell goes over the max voltage. It also does bottom balancing.
Heaps of wires & heaps of connections though & no way of telling which cell triggered a fault condition.
It would be very nice to have a digital setup especially via the LCD display.
Smaller, less wires (mine was a nightmare), more diagnostic info & easily changeable parameters.

[harlequin2]

Yeah, I know what you mean about the wires. My original bms and the one that is currently fitted to my car uses an 8-cell board with an Atmel micro. It has a couple of LM324s to level shift and condition the cell voltages which are read by the 8-channel ADC. Each board has opto-coupled comms on a multidrop bus. It works OK but its a nightmare with a wire from each cell running off to a number of Molex connectors. It scares me just looking at it! Also, the regulations here now require you to have a fuse in each sense wire and that is just too difficult. The cell module bolted directly to the terminals doesn't require a fuse, although I have provided one by way of a bit of skinny track.
I'll send you a copy of the document describing how it works.

[jackbauer]

harlequin2 , could you clarify why Adam's charger is illegal? You mean its non isolated?

Regards the bms i'll be watching this thread with interest. As yet I have not seen a design that I would feel safe about having installed on my pack. Commercial or DIY. So far the best idea I have heard floated about involved wireless comms. Then that introduces its own set of issues. Round and round......

ianbartie , I too built the battery vehicle soceity bms. Seemed ok on the bench so I installed it in the car one morning. Lets just say it was back out by afternoon!

[sawickm]

Originally Posted by harlequin2

Maybe I'll put something in the s/w so the user can choose either SLA or Li, if there's any interest shown. Its only a matter of changing the range the ADC works over and altering the master s/w to suit.

I have a description of the way the whole thing works, but the .pdf file is way too big to add here as an attachment.

I would be interested in a dual mode BMS (Lion/SLA). No one has a BMS like that !!!

Not many SLA BMS's on the market. Manzanita Micro has a MK3 BMS a voltage controlled bypass regulator with digital interface Manzanita Micro. Volt Blocher had a bypass shunt BMS, but went out of business.

When you get to the point you want to add BMS PDF files to the ReVolt wiki, PM me for my email address and I'll add them to my file server.

-Mark

[harlequin2]

Originally Posted by jackbauer

harlequin2 , could you clarify why Adam's charger is illegal? You mean its non isolated?

That is the big issue. Non-isolated appliances are NOT permitted at all. You can argue that the voltage outputs are lethal anyway, but "roolz is roolz" and you can't win against bureaucracy. Nothing to stop you making and using one yourself (except that it is illegal), but if anyone was to be electrocuted, you would be liable for prosecution. Not worth the risk.

Wireless comms would/might be good but expensive. This is using optical comms! The fact that the connections are long-ish is beside the point - I hope. As I said, I've tried it with one cell module in my car and it works OK. Hope to have enough pcbs to fit every cell shortly.

[harlequin2]

Originally Posted by sawickm

I would be interested in a dual mode BMS (Lion/SLA). No one has a BMS like that !!!

Not many SLA BMS's on the market. Manzanita Micro has a MK3 BMS a voltage controlled bypass regulator with digital interface Manzanita Micro. Volt Blocher had a bypass shunt BMS, but went out of business.

When you get to the point you want to add BMS PDF files to the ReVolt wiki, PM me for my email address and I'll add them to my file server.

-Mark

Well, probably no-one would make a SLA cell module. I still don't see how you would use it with most 12V batteries taht I have seen having the cell interconnections buried in plastic or other goop.

I'll be in touch when I have files available. (I have the cell module boards pretty well finalised and I am using them with a laptop, but the "master" needs finishing off to make it a complete system).